This invention is concerned with the extraction of bitumen from tar sands.
Approximately 30 billion barrels of tar sand bitumen in Athabasca (out of 625 billion barrels in Alberta) and part of 26 billion barrels in Utah are accessible to mining. Tar sands are essentially silicious materials such as sands, sandstones or diatomaceous earth deposits impregnated with about 5 to 20% by weight of a dense, viscous, low gravity bitumen. The mined sands are now commercially processed for bitumen recovery by the "Clark Hot Water" method. In the Athabasca region, it has been estimated that, at most, two additional plants of the 125,000 bpd size can make use of this recovery technique; this restriction stems from severe environmental constraints such as high water and energy consumption and tailings disposal. Two alternate bitumen recovery methods are being pursued: thermal treatment (e.g., retorting) and extraction with solvents. Both have high energy requirements; the first--poor sensible heat recovery and the burning of part of the resources, and the second--solvent-bitumen separation and solvent loss through incomplete steam stripping. Shortcomings of these approaches are minimized by the present process. Finally, Utah tar sand and minable resources in the Athabasca region are both recoverable by this method.
Various types of thermal (pyrolysis) processes and solvent extraction processes have heretofore been used to extract synthetic crude from tar sands. Some of the thermal processes presently known involve the use of a variety of horizontal or vertical retort vessels or kilns for the retort. In particular the Lurgi-Rhurgas process uses a mixing screw-type retort and the Tacuik process uses a rotary kiln-type retort. Some of the solvent extraction processes presently known are the Western Tar Sand processes described in the U.S. Pat. Nos. 4,054,505 and 4,054,506 which includes the use of ultrasonic energy, the CAG (Charles-Adams-Garbett) process using a water-base extraction, and the Randall process using hot water. Past practices have generally involved the use of either a thermal process or a solvent extraction process.
Applicant's copending application, Mobil Docket No. 7757, entitled "Method for Extracting Oil From Oil-Contaminated Soil" and commonly assigned, discloses a method similar to the present invention for extracting oil from oil-contaminated soil using a solvent and sonic energy in the low frequency range of 0.5 to 2.0 kHz.
U.S. Pat. No. 2,973,312 discloses a method of removing oil from sand, clay and the like, including employing ultrasonic vibration and a solvent.
U.S. Pat. Nos. 4,054,505 and 4,054,506 disclose a method of removing bitumen from tar sand using ultrasonic energy.
U.S. Pat. No. 4,151,067 discloses a method for removing oil from shale by applying ultrasonic energy to a slurry of shale and water.
U.S. Pat. No. 4,304,656 discloses a method for extracting oil from shale by employing ultrasonic energy.
U.S. Pat. No. 4,376,034 discloses a method for recovering oil from shale employing ultrasonic energy at frequencies between 300 MHz and 3,000 MHz.
U.S. Pat. No. 4,443,322 discloses a method for separating hydrocarbons from earth particles and sand employing ultrasonic energy in the frequency range of 18 to 27 kHz.
In U.S. Pat. No. 4,495,057 there is disclosed a combination thermal and solvent extraction process wherein the thermal and solvent extraction operations are arranged in parallel which includes the use of ultrasonic energy.
U.S. Pat. Nos. 4,765,885 and 5,017,281 disclose methods for recovering oil from tar sands employing ultrasonic energy in the frequency range of 5 to 100 kHz and 25 to 40 kHz respectively.
U.S. Pat. No. 4,891,131 discloses a method for recovering oil from tar sands employing ultrasonic energy in the frequency range of 5 to 100 kHz.
In contrast to the prior art, in the present invention mined tar sands containing bitumen are mixed with a solvent to form a tar sand/solvent slurry, the upwardly flowing solvent e slurry is fed into the top of a vertically disposed acoustic chamber and fresh solvent is injected into the bottom of the acoustic chamber and flows upwardly at a controlled rate whereby the particles of tar sand fall by gravity through the solvent and are subjected to sonic energy in the low frequency range of 0.5 to 2.0 kHz whereby the bitumen is removed from the tar sand and dissolved by the upwardly flowing solvent without cavitation of the solvent.